During mitosis, when does cleavage form? Does it form near the end of telophase or near the beginning?
During mitosis, cleavage forms near the end of telophase. Cleavage refers to the process of cytokinesis, where the parent cell divides into two daughter cells. It involves the formation of a contractile ring composed of actin and myosin filaments, which constricts and eventually pinches the parent cell into two separate daughter cells.
To understand this, let's break down the stages of mitosis. Mitosis consists of several stages: prophase, prometaphase, metaphase, anaphase, telophase, and cytokinesis. During prophase, the chromatin condenses to form visible chromosomes, the nuclear membrane disintegrates, and the spindle apparatus begins to form. In prometaphase and metaphase, the chromosomes are fully condensed and aligned at the center of the cell.
During anaphase, the sister chromatids of each chromosome separate and move towards opposite ends of the cell, pulled by the spindle fibers. This is followed by telophase, where the separated chromatids reach the poles of the cell, the nuclear membranes start to form around the separated chromosomes, and the spindle apparatus begins to disintegrate.
Finally, cleavage occurs during cytokinesis, which is the last stage of mitosis. Cleavage starts near the end of telophase when a contractile ring forms at the equator of the cell, also known as the cleavage furrow. The contractile ring contracts, causing the plasma membrane to inte inward and progressively deepen. Eventually, the plasma membrane pinches off completely, dividing the parent cell into two daughter cells.
So, in summary, cleavage forms near the end of telophase, as part of cytokinesis, and involves the formation of a contractile ring that leads to the division of the parent cell into two daughter cells.